Urinary hydroxyproline to creatinine ratio as a biological effect marker for exposure to NO2 and tobacco smoke

In order to study the relationship between NO₂ exposure and effects, we monitored personal NO₂ exposures and the hydroxyproline to creatinine ratio in urine of about 800 women in two communities near Tokyo. Monitoring was conducted during two seasons, winter and summer 1982. The hydroxyproline to creatinine ratio (HOP:C) was determined from urine samples collected in the early morning. Daily average personal NO₂ exposures (ENO₂) were measured by using a filter badge.In both seasons, HOP:C was found to have significant correlation with ENO₂ and active and passive smoking. In addition, subjects living near major roads had significantly higher HOP:C levels in the summer compared with those living far from them. We hypothesize that these higher HOP:C levels in the summer were due to higher air exchange rates resulting in infiltration of automobile exhaust into homes. ENO₂, however, did not correlate with either the distance of the subject's house from major roads or with the amount of smoking. Stepwise multiple regression analysis revealed that HOP:C could be predicted by personal NO₂ exposures and smoking variables with a high level of confidence.